1. Technical Field of the Invention
The present invention relates to an output of signals synchronized in terms of frequency.
2. Related Art
Making repetition frequencies of optical pulses output from two lasers coincident with each other has conventionally been known (refer to FIG. 13 of a patent document 1).
As relevant documents, patent document 2, and non-patent documents 1-6 can be listed.    (Patent Document 1) Japanese Laid-Open Patent Publication (Kokai) No. H10-96610    (Patent Document 2) PCT Pamphlet W02006/92874    (Non-Patent Document 1) Bartels et al, “Ultrafast time-domain spectroscopy based on high-speed asynchronous optical sampling”, Rev. Sci. Instrum., vol.78, pp.035107 (2007)    (Non-Patent Document 2) T. Yasui et al, “Asynchronous optical sampling terahertz time-domain spectroscopy for ultrahigh spectral resolution and rapid data acquisition”, Appl. Phys. Lett., vol.87, pp.061101 (2005)    (Non-Patent Document 3) A. Bartels et al, “High-resolution THz spectrometer with kHz scan rates”, Optics express, vol.14, pp.430 (2006)    (Non-Patent Document 4) A. Bartels et al, “Femtosecond time-resolved optical pump-probe spectroscopy at kilohertz-scan-rates iver nanosecond-time-delays without mechanical delay line”, Appl. Phys. Lett., vol.88, pp.041117 (2006)    (Non-Patent Document 5) C. Janke et al, “Asynchronous optical sampling for high-speed characterization of integrated resonant terahertz sensors”, Optics Letters, vol.30, pp.1405 (2005)    (Non-Patent Document 6) Y. Takagi et al, “Subpicosecond optical sampling spectrometer using asynchronous tunable mode-locked lasers”, Rev. Sci. Instrum., vol.70, pp.2218 (1999)